Navigation instrument



April 19, 1949.

R. L. WATHEN NAVIGATION INSTRUMENT me@ Juri'e 9,4944' 2 Sheets-Sheet 1 Kliff/VIR INVENTOR Raaf/wl. Mnl/EN ORNEY April 19, 1949. R. l.. wATHEN NAVIGATION INSTRUMENT 2 Sheets-Sheet 2 Filed June 9, 1944 INVENTOR ATTORNEY M m m L m m R Patented Apr. 19, 1949 NAVIGATION INSTRUMENT Robert L. Wathen, Hempstead, N. Y., assignor to The Sperry Corporation, a corporation of Dela- Ware Application June 9,1944,l serial No. 539,403

(ci. 1v1-95) y 6 Claims. l

This invention relates to navigation instruments and more particularly, to an instrument for assisting an aircraft pilot in making instrument landings. l

It is customary when navigating a craft, tovemploy electromagnetic means for defining a path or route over which the craft is to travel, and to provide the pilot with visual means for denoting the relation of the craft to the predetermined path. Although various types of electromagnetic systems may be employed for describing the desired path, based on the directional characteristics or the propagation rate of electromagnetic energy, the present invention is herein described as applied to a conventional equi-signal system of directive radiation, and specifically to such a system having beams overlapping in a vertical plane for defining a glide path useful in conjunction with instrument landing operations. l

As is well known, equi-signal systems utilize intermittently energized and distinctively modulated and partially overlapping lobes of electromagnetic energy, the axis of which defines an equi-signal locus or path along which the craft is to travel. A zero center type meter is energized in opposition by signals derived from the respective lobes, the meter providing a neutral indication when the signals are balanced, vto denote Deviation that the craft is properly on course. of the craft from its course, unbalances the derived signals and produces a meter reading ordinarily proportional to the deviation angle, representing the difference between the instantaneous bearing of the transmitting station and the heading of the equi-signal locus.v By the use of specially designed automatic volume control (A. V. C.) circuits, it has been found possible to indicate craft displacement substantially in terms of linear transverse departure, irrespective of the distance between the craft and the transmitting station'. Since the displacement reading ordinarily`is a function of the deviation angle, and the deviation angle in turn varies for a given lineardisplacement from course as a function of the distance fromthe transmitting station it was found that to produce a reading of linear displacement required the use of over-compensated or forward-acting A. V. C. circuits, to decrease the strength of the output signals as the. carrier strength increases.

The present invention has for its principal purpose to provide the pilot of a craft with an indication not only of his relation to a predetermined path or course, bat to combine such an indication with a reading of his relation to an independent reference, typically a reference surface such as the ground at sea level, the projected elevation of a landing path or the subjacent terrain. If the indicator or meter is calibrated in linear units as previously described, in order to denote actual linear displacement from the chosen path, the same meter may be utilized to denote linear displacement from the chosen reference surface. More specifically, if the indicator is calibrated to denote roughtly the distance of an aircraft above or below a glide path, such an instrument may be utilized to denote some function of the 4aircrafts altitude as ground clearance or barometrically-determined altitude.

The principal objects of the present invention are. to provide a navigation instrument indicating ldisplacement of a craft from a predetermined path and from an arbitrarily chosen reference; to provide a navigation instrument denoting in substantially linear units displacement of the craft from a predetermined path and from a reference surface; to provide an improved instrument landing meter indicating displacement from the landing path and an alti-- tude function suchas ground clearance; to provide an improved cross pointer meter having a. vertical scale in linear units for denoting vertical displacement of an aircraft from a glide path, and also for indicating the instantaneous altitudeof the aircraft; to provide in an instrument landing meter an indication of ground clearance with the ground represented by a movable mask member;l to provide in a navigationA instrument an indication of linear displacement of the craft from course, with an index simulating the craft. drawn to the scale defined by the linear units. These'and other objects will become more fully apparent from the following description and from the accompanying drawings.

In the drawings,

Fig. 1 is a diagrammatic view of a navigation instrument such as a cross pointer meter together with receiving equipment, adapting the meter to indicate displacement of the craft from a landing path, and ground clearance; y

Fig. 2 is a block diagram of the system shown in Fig. 1, the components of the receiver being shown in greater detail;

Fig. 3 is a diagrammatic view of one form of ground clearance or altitude control;

Fig. 4 is a. vertical cross sectional View through one form of meter wherein gyroscopic stabilization'is included;

Pil. 5 is a detailed sectional view taken along the line l-l of Fis. 4; and

Fig. 6 is a diagrammatic view of a modified of ground clearance or altitude indication control.

Generally speaking, the invention comprehends providing an indication of displacement of a craft from a predetermined path in linear scale units, and providing on the scale an indication of craft displacement from an independent reference line or surface such as thesubjacent terrain or the projected sea level. The principles of the invention are applicable generally to all sorts of dirigible craft being guided along an electromagnetically or otherwise dened path. Although the invention is in nowise `thus limited, to simplify the illustration, it is herein disclosed as specifically applied to an equi-signal type instrument landing system.

As shown in Fig. 1, use may be made of a receiver responsive to some characteristic of the electromagnetic energy defining the predetermined dirmection of travel, for deriving therefrom signals representative of displacement of the craft from the path, and a meter or indicator M provided with scale means for denoting the displacement of the craft, preferably in linear units. In the specified arrangement disclosed, the meter M comprises a conventional cross pointer meter, having a pair of crossed pointers I I and I 2 responsive to vertical and horizontal displacement signals, respectively, from the receiver. yFor indicating the actual displacement of the craft from the equi-signal locus as a function of the distanceV between the pointer intersection and a reference index member I3 representative of the craft, dial I is provided with suitable scales I4, I4 calibrated preferably in linear units. As applied to instrument landing, the scales may be calibrated to denote vertical and horizontal displacement respectively, with maximum displacement of the order of two hundred feet. If the index member I3 comprises a representation of the craft in which the receiver is mounted, and the scales are in linear units, it is proposed to make the representation roughly to scale, so that the pilot may judge his displacement more reliably, for example as a function of the wing span of the craft. A ground clearance meter or other distance measuring device D provides a signal representative of the distance between the craft and the ground or other reference. A mask member I coupled to altimeter controlled means 32 is responsive to the signals from the device D and cooperates with the scale I4 to provide the proper indication, as will more fully appear.

The apparatus of Fig. 2 discloses in block diagram form, a generally conventional superheterodyne receiver, having separate reception channels for the respective characteristically modulated components of the overlapping electromagnetic lobes defining the localizer and glide paths of an instrument landing system. The receiver comprises the usual preamplifier and converter I6, intermediate frequency amplifier II, detector I3, and audio amplifier I9 for feeding the signals into band pass filters 2| and 22 where the respective modulation components are segregated for rectification by rectiers 23 and 24 for comparison across an output resistor 25. The respective lobes for the `glide path and localizer path may employ the same modulation frequencies, typically 600 and 900 cycles per second, to define the equi-signal locus. However, the carrier frequency for the lobes defining the glide path in practice.

customarily is separated conveniently from the carrier frequency used for the lobes defining the localizer path. This provision, and the use of different intermediate frequencies, avoids interference between th'e separate channels of the receiver. An A. V. C. generator 26 derives energy from the incoming signals and develops a voltage characteristic of the carrier strength, 'which voltage is applied to the control elements of the intermediate amplifiers in a conventional manner. It has been determined recently, that if the A. V. C. voltage is applied additionally to a sufficient number of stages in the audio amplifier I3, that the output power may be made to vary as a decreasing function of the carrier strength. It will be apparent that the over-correction of output power may be sufficient to transform the meter readings from the usual angular displacement indications to the more convenient linear displacement indications. This expedient is obtained by varying the receiver gain as the square of the distance between transmitter and receiver, a condition that has been closely approximated Accordingly, at any distance from the transmitting station, the pilot may determine the corrective motions required to restore the craft to its course, according to the location of the pointer intersection relative to the index I3, and the amount of correction required may be judged from the horizontal and vertical distance between the intersection and the index member I3 as determined by the scales I4, I4'.

Either or both the horizontal or vertical displacement calibrations of the scales I4, I4 may be utilized to indicate distance of the craft from a reference point line or surface. Thus the vertical scale denoting displacement from the glide path, may be utilized to denote ground clearance or altitude. A simple arrangement for producing this result is disclosed in Fig. 3 and comprises an altitude sensitive device, such as an evacuated Sylphon bellows 3i functioning as an aneroid barometer to denote altitude as a function of barometric pressure. Although the bellows motion may be used directly through a mechanical linkage to denote altitude as indicated in Fig. 6, as will appear, it may be desirable to minimize frictional error by utilizing some simple servo mechanism. Such a device, as shown in Fig, 3 may comprise an indicator 32, electrically controlled in response to axial motion of the stem 33 of the bellows 3l. The stem 33 may actuate the movable arm 34 of a variable resistor or other suitable control element 35 capable of regulating electrical energy applied to the indicator 32 from a power source such as battery 36. The type of indicator 32 employed may vary widely, and depends in some measure on the nature of the meter M. It has been common practice to utilize a cathode ray tube in the meter M to form images on the scale thereof displaced from a reference mark or index as a function of the signals derived by the receiver. More customarily, however, the meter M utilizes movable pointers II and I2 actuated by separate meter movement assemblies 31 and 38. Similarly with the indicator 32, use may be made of electrostatic deflection in a cathode ray tube meter,`

or as indicated of a DArsonval movement 39, the current to which ows from the source 36 in accordance with the position of the arm 34. The movable element of the indicator 32 may comprise a conventional pointer or arm 4I cooperative with the scale I 4 to denote altitude or ground clearance. Preferably, however, the mask member I5 is attached to the arm 4I to provide a more realistic 32 is adapted to that specic purpose. The mask member conveniently comprises a sheet of colrepresentation of the ground when the indicator scale.` The pilot may thus compare the altitude or ground clearance indication with a known proper altitude of the craft, e. g., at the moment ored transparent material, through which the i Aprovide substantially perpendicular pointer inv tersection. The mask member I likewise may be shaped to conform to the curved surface of the dial.

The structural relationship between the parts is most clearly shown in Fig. 4. The meter M is shown enclosed in a suitable casing 42 adapted for mounting in the instrument panel of an airplane or other dirigible craft. The front of the casing is provided with a circular opening protected by a lens or cover 43 of glass or other transparent material through which the scales I4, I4', mask I5 and pointers II ,and` I2 arevisible. The meter movement assemblies 31 and 38 may be supported by the casing 42 with axes disposed along perpendicular diameters of the spherical shell segment dened by the curved dial I0.

The mask member I5 may be supported as shown in Fig. 4 for movement behind a transparent dial I0, and thel interior of thev casing 42 may be illuminated by a small lamp 44. Likewise, any or all Aof the elements comprising the pointers II and I2 and index member I3 may be transparent and may be mounted in front or behind the dial I0, as desired. The arm 4I is pivoted to the casing 42 as shown in Fig. 5, as bymeans of sleeve 45 `extending inwardly from the casing.

the usual marker beacon signals are received. Thus, when the pilot receives the'outer marker beacon signal, he may make any necessary adjustment of the altitude indicator by moving mask member I5. The altitude reading then may be checked when the inner marker beacon signal is received. A similar manual control element 64 is shown in Fig. 3 and comprises'l merely a variable resistor in series with the resistor 35 and the source 36. v

Fig. 6 discloses a simple mechancalcontrol of the mask member I5 in response to axial movement of the stem 33 that may be employed where frictional losses are small, and comprises merely step-up gearing65, interconnecting sector 55 and A ball-bearing 46, and an adjustable counterbalance 41 may be employed to render the ground clearance or altitude indicator more sensitive.

Convenient mechanism is employed to operate the mask member I5 in response to a control device such as bellows 3|. In the arrangement shown in Fig. 4, the motion of the stem 33 in response to altitude changes may be transmitted to the indicator 32 through a rack 48 and pinion 49, through a suitable servo mechanism preferably including a self-synchronous transmitter 5I and receiver 52, having a servo motor 53 responsive to phase sensitive amplier 54. A gear sector 55,

pivotable with the arm 4I is moved by the motor 53 through a suitable gear train 56. A followback, such as a gear 5l, erases the motor-driving signal when the transmitter 5I and receiver 52 are electrically aligned. It will be apparent from the foregoing, that a change in altitude produces an axial motion of stem 33, causing a signal to be generated by the transmitter 5I for operating motor 53 to bring the receiver 52 into alignment. The resultant motion of sector 55 is imparted to the arm 4I through a clutch 58, as will appear, to provide the proper altitude indication.

It is desirable to adjust the mask member I5 of indicator 32 relative to the scale I4, both when initially Calibrating the instrument, and when readjusting, e. g.) so as to compensate for varying barometric pressures. Asimple manual adjustment is shown in Fig. 5 and comprises a friction clutch 58, normally loaded by a compression spring 59 so as to hold the hub 62 of arm 4I against the hub 63 ofV `gear sector 55. An adjustment knob 6I extends through the sleeve 45 and is attached securely to the hub 62. By depressing the knob 6I, the clutch 58 is disengaged and by rotating the knob, the mask member I5 may be shifted to any desired position on the rack 48. With such an arrangement, a slight motion of the stem 33 produces an appreciable motion of the gear sector 55.

As shown in Fig. 4, a gyro vertical 66 may f used to stabilize the instrumentabout the craftv roll axis. Although thescales I4, I 4', pointers II and I2 and mask I5 may be stabilizedagainst rolling motion of the craft, and the banking angle may be denoted by reference to permanently mounted index member I3, it is preferred for purposes of the present disclosure to mount the index member'l3 on to the gyro vertical for stabilization about the roll axis and to ldenote the banking angle by reference to the scale I4, pointer assembly and mask member I5 which tilt with the craft. As'shown in Fig. 4, the index member I3 is supported Vin the center of the scale I4 by a slender rod 61, preferably transparent, extending over the top of the dial I0 for mounting on gimbal ring 68 of gyro vertical 66. Accordingly, as the craft banks, the index member I3 -appears to the pilot as though it tilted, and the amount of the apparent tilt corresponds to the banking angle of the craft.- The pilot thus is able, by observing a single instrument, to be continuously and fully informed as to the position of the craft relative to the desired path, as to any abnormal banking angle that might render a normal landing diicult and as to theposition of the ground with respect to the plane. The craft approaches the landing strip by proceeding along the glide path. Beyond a predetermined' altitude established by the full scale displacement reading of meter M, the mask member I5 progressively rises over the scale I4 informing the pilo-t that he is nearing the landing point,

thereby allowing him to take Whatever appropriate measures are required during the landing operation.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made Without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What-is claimed is:

l. An aircraft instrument for indicating the aircraft position relative to a predetermined glide I path and to the ground, comprising a first movable indicating element, means for varying the height of said rst indicating element above or below a reference position in said instrument according to the displacement of the aircraft position below or above the predetermined flight path. a second'indicating element, and means for craft.

varying the height of said second indicating element beneath said reference position according to the proximityof the aircraft position to the ground level, said means for controlling the height of said iirstindicatingelement beingso arranged that said ilrst indicating element occupies the reference position when the aircraft position is on said path and said means for controlling the height of said second indicating element being so arranged that said second indicating'element rises to said refcrence position as the position descends to the ground level, whereby the distance of said reference position above said second indicating element represents the height of the aircraft position above the ground and the distance of said first indicating element above said second indicating element represents the height of said path above the ground and the positional relation of said reference position with both said indicating elements therefore represents the simultaneous positional relation of the aircraft with the ground and the path.

2. Aircraft guidance apparatus as defined in claim 1, wherein said second indicating element presents a substantially horizontal portion indicating the generally level ground surface, said apparatus further including means for stabilizing said second indicating element against the roll of the aircraft, whereby said second indicating element realistically indicates the height and general orientation of the ground beneath the air- 3. An aircraft instrument for cooperating with an instrument landing glide path receiver and for indicating the craft position in reliance upon the output of the receiver, the instrument comprising a frame, first indicating element movably supported in said frame, voltage responsive mechanism coupled to said indicating element and adapted to vary the height thereof in said frame according to the instrument landing glide path receiver output voltage to represent the vertical displacement of an instrument landing glide path from the aircraft position, a second indicating element arranged to represent the ground surface area. generally below and ahead of the aircraft, and means connected to said second indicating element for varying the height thereof inversely according to the height of the craft position above the ground, whereby said apparatus is capable of presenting to the pilot of the aircraft a fully correlated pattern scalarly showing the relative positions of the ground surface, the aircraft and the glide path in such a natural arrangement l that the pilot is enabled to rely fully and solely 5 upon this apparatus not only for travelling along the glide p'ath but also for guarding against unexpected contact with the ground.

4. Apparatus as defined in claim 3 further ,1licluding means for stabilizing said further indicating element about an axis parallel to the roll axis of the aircraft.

5. A craft guidance instrument comprising a housing, first and second crossed indicating members movable in said housing, means for deecting said members in such a way as to provide for universal movement of their point of intersection throughout a zone of Aappreciable area, a mask movably supported in said housing and having a border movable in close adjacency to said zone,

and means for providing translational movement of said mask relative to said crossed members for indicating a limitation of the safe range of craft navigation.

6. lA craft guidance instrument comprising a housing, first and second crossed indicating members movable in said housing, said members having arcuate visible portions and being pivoted about substantially intersecting and substantially perpendicular axes, the region of intersection of the pivotal axes being in the vicinity of the centers of curvature of said arcuate portions, and a mask formed substantially according to the surface of a spherical section, said mask being pivoted for movement about an axis substantially in the plane of said pivotalaxes and passing substantially through said region of intersection of said pivotal axes, the radius of said mask and the radii of said arcuate portions being of the same order of magnitude.

ROBERT L. 'WATHEN REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 791,785 Hertzberg et al. June 6, 1905 840,569 Lea Jan. 8, 1907 1,275,786 Stuart Aug. 13, 1918 1,981,589 Dunmore Nov. 20, 1934 1,991,892 Fessenden Feb. 19, 1935 1,999,047 Hahnemann Apr. 23, 1935 2,225,046 Hunter Dec. 17, 1940 2,226,930 Hefele Dec. 31, 1940 2,235,390 Smith Mar.- 18, 1941 2,262,245 Moseley et al. Nov. 11, 1941 2,264,063 Bond Nov. 25, 1941 FOREIGN PATENTS Number Country Date 538,214 Great Britain July 24, 1941 Certificate of Correction Patent No. 2,467,412 April 19, 1949 ROBERT L. WATHEN It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 7, line 11, before the Word position, second occurrence, insert aircraft;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 25th dey of April, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

